Applying the Ellipse Tool (U) make one more roundness:



Blending Options>Gradient Overlay:

 

 



Blending Options>Inner Glow:

 



Blending Options>Drop Shadow:

 



Blending Options>Stroke:

 



We have to picture now the power supply indicator. Select for this operation the Custom Shape Tool (U).



Choose now the Rectangle Tool (U) and press the Alt button for erasing and Shift button for adding it, try to represent the indicator the way it is shown next picture: